The present disclosure relates generally to a line-voltage detection method for a power controller with high-voltage startup, and more particularly to brown-out protection and brown-in mechanism of a power controller with high-voltage startup.
A line voltage normally refers to the voltage generated by rectifying an alternating-current (AC) voltage from a power grid, it is a direct-current voltage (DC), and its value always provides important information to AC-to-DC power supplies or converters. For example, when a line voltage sags, a power supply powered by the line voltage might need to stop its power conversion, otherwise disasters could happen due to malfunction caused by the sag. This kind of protection is known as brown-out protection. In the other hand, based upon the detection or a line voltage recovering from sagging, a power supply equipped with brown-in mechanism could resume its power conversion automatically and supply power to its load properly. Furthermore, the awareness of the value of a line voltage could be used to compensate outcomes of a power supply that are otherwise influenced by the line voltage.
FIG. 1 demonstrates an AC-to-DC power supply 100 with a flyback topology. Bridge rectifier 12 provides to an AC voltage VAC-MAIN from a power grid full-wave rectification to generate input voltage VIN at input node IN. Power controller 18, normally a packaged integrated circuit with pins, provides pulse-width modulation (PWM) signal SPWM to control power switch 26, which in response controls a current flowing through transformer 16. When the power switch 16 is turned ON, transformer 16 energizes; and when it is turned OFF, transformer 16 de-energizes to, via diode 32, buildup output voltage VOUT over output capacitor 30 that powers load 19.
Diodes 14 together perform half-wave rectification to generate line voltage VLINE. Power controller 18 has a pin, named high-voltage node HV hereinafter, connected to line voltage VLINE via current-limiting resistor 20. Power controller 18 is equipped with high-voltage startup technology. When AC-to-DC power supply 100 is just connected to the AC voltage VAC-MAIN, a high-voltage startup procedure commences, power controller 18 pulls a charging current from high-voltage node HV, this charging current is directed to go through operating voltage source node VCC and charge operating voltage capacitor 28, so operating voltage VCC is built. Once operating voltage VCC is high or good enough, the high-voltage startup procedure concludes, the charging current stops, and power controller 18 starts providing PWM signal SPWM.
FIG. 2A shows power controller 18a that detects line voltage VLINE and is capable of performing brown-out protection. Power controller 18a could replace power controller 18, and has a high-voltage startup transistor 46, which is turned ON during the high-voltage startup procedure to provide the charging current charging operating voltage capacitor 28. External to power controller 18a, connected between high-voltage node HV and ground line GND is voltage divider 40a consisting of resistors 42a and 44a. A joint node between resistors 42a and 44a is connected to sense node SENS of power controller 18a and provides to power controller 18a fraction result of line voltage VLINE. The architecture shown in FIG. 2A provides flexibility to power supply system designers, who could easily change brown-out and brown-in references for brown-out protection and brown-in mechanism by selecting different resistances of resistors 42 and 44. Brown-out reference means the reference voltage for line voltage VLINE to goes below and to trigger brown-out protection; brown-in reference means the reference voltage that line voltage VLINE must exceed to start brown-in mechanism.
In view of bill-of-materials (BOM) cost, that architecture in FIG. 2A is expensive however, because resistors 42 and 44 are two discrete components that require extra storage management and device assembling. Furthermore, power controller 18a need dedicate an additional pin, which is sense node SENS.
Another detection method for line voltage VLINE is to embed voltage divider 40a of FIG. 2A in a power controller, as demonstrated by power controller 18b in FIG. 2B. In comparison with power controller 18a of FIG. 2A, power controller 18b in FIG. 2B has embedded voltage divider 40b inside itself, and requires no pin for sense node SENS. A power supply based on power controller 18b could be cheaper, but possibly in the expenses of the flexibility to the modification of brown-out and brown-in references. Power supply system designers could not change the brown-out and brown-in references for brown-out protection and brown-in mechanism once the power controller 18b is fabricated.